(1) Field of the Invention
This invention pertains to the field of radar simulators.
(2) Description of the Prior Art
Probably the oldest and most remotely related prior art is the acoustic water-tank trainer in which a modification of sonar equipment was used to scan submerged models of terrain. The difference in propagation speed between electromagnetic radiation in air and sound in water provided a reasonable scale factor, and war-inspired ingenuity led to such novelties as the use of powdered effervescent digestant tablets to simulate chaff or window by their bubbles. The device was clumsy in dimensions and inflexible in that terrain representations had to be modeled physically. Somewhat simpler in that the terrain is simulated by transparencies, and so may be produced and replaced economically, and need not be inconveniently large, is the system employing e.g. flying-spot scanners, of which U.S. Pat. No. 3,355, 538 of Thomas et al. is an example.
U.S. Pat. No. 3,446,903 of B. Beizer discloses a radar trainer relying upon data stored digitally, as in a magnetic tape, drum, or disk store which is converted into a scope representation. Beizer mentions at his column 4, lines 14 and 15 that weather noise may be represented by a simple random noise signal insertion.
U.S. Pat. No. 3,514,521, Burchard et al. discloses a radar trainer intended primarily to train marine navigators, and so having fixed targets defined completely by stored data.
Warnock, U.S. Pat. No. 3,602,702; Romney et al., U.S. Pat. No. 3,621,214; and Erdahl et al., U.S. Pat. No. 3,665,408 teach means for presenting visual perspective representations of objects described by stored numbers; and they teach adjustment of the illumination of faces of such objects according to some assumed mode of illumination. However, they aim at representing an object viewed by the eyes; so they do not encounter the problem that the reflective characteristics of a surface must be simulated canonically; any geometrical features of a surface in their images must be described in detail, quite literally "by the numbers".
Thompson, U.S. Pat. No. 3,550,407, describes a means of simulating ground clutter for testing of airborne moving-target-indicating radar systems on the ground. It has no pertinence to the present invention.
U.S. Pat. No. 3,700,780, Roeschlein, is aimed at testing sonar devices by providing (column 1, lines 48 et seq.)" . . . a plurality of single bit outputs of different delays to simulate a received sonar wavefront from a simulated target relative to the sonar receiver."
Heartz, U.S. Pat. No. 3,769,442, while not directly pertinent to the present invention, is of interest in the general field of computer generation of images.
U.S. Pat. No. 3,783,172, of Bernstein, discloses a radar simulator in which target data on a particular bearing are entered into a register in order of increasing range from the radar set, and are then read out and converted into video signals to drive a radar set.
U.S. Pat. No. 3,800,440 of Membrino et al. discloses a simulator of conventional IFF signals. It uses shift registers for this prupose, and applies the IFF simulations to a radar set.
In summary, none of the prior art known to the applicant teaches the use of fedback shift register outputs representing a plurality of successively timed outputs, displaced in time to be simultaneous, to provide characteristic "texture" of radar returns for given kinds of terrain.